The invention relates generally to roll apparatus for treating webs of material and, more particularly, to an improved quick release device for separating individual rollers of the apparatus.
A roll apparatus having a quick release device is disclosed in DE-PS 3622398, which shows a calender equipped with a quick release device permitting adjacent rollers to be separated from each other to avoid damaging a "soft" roller should a defect in the paper web, for example, a fold or a tear appear. A "soft" roller, as known in the art, is a roller provided with an elastic covering, such as paper or plastic. At least the bottom roll in such a calender is constructed as hydraulically supported roll in which a hollow cylinder rotates about a stationary crosshead and is supported on the crosshead by a hydraulic supporting device, which produces the line pressure. The crosshead is supported at its distal ends, which project from the hollow cylinder, by hydraulic force exerting devices comprising hydraulic cylinders. During operation, the crosshead bends inside the hollow cylinder under the pressure transmitted to it by the hydraulic supporting device and, consequently, stores a quantity of elastic energy. Thus, at the same time, the crosshead is affected by the simultaneous action of two hydraulic devices, which are independent of each other. If, without the provision of any special measures, the pressure in the hydraulic supporting devices drops suddenly during a quick release action of the bottom roll and the elastic energy of the bent crosshead is released, very powerful strokes, i.e., movement of the crosshead within the cylinder, can occur, which may have a destructive effect upon the roll apparatus.
To counteract this effect, the hydraulic supporting device of DE-PS 3622398 is relieved according to a specific time sequence. The hydraulic supporting device in the hollow cylinder comprises a series of piston-like support elements, which are guided in cylinder bores in the crosshead and are pressed by hydrostatic pressure against the inner circumference of the hollow cylinder. To effect the quick release action, the pressure in the support elements is initially lowered, after which a pressure loss in the hydraulic force exerting devices occurs after an interval determined by a time delay element has passed.
The problem with such an arrangement is that the forces acting on the roller have a direct effect upon the quick release action, while controlling the pressures only has an indirect effect. Thus, even if the pressure in the hydraulic supporting device, i.e., in the individual support elements, has already dropped before quick release occurs, these elements still can transmit considerable forces. This is due to the fact that during a pressure relieving displacement of the support element friction occurs between the individual support elements and the crosshead. Therefore, for a moment, forces still act between the hollow cylinder and the crosshead, which can produce the undesirable and possibly destructive strokes of the crosshead.